How to Buy Characters?
This can only be done while you’re in Free Play mode (it doesn’t work in Story mode). You can only buy a character that you have already unlocked, by holding the Triangle button on PS4 / holding the Y button on Xbox One / holding the X button on Switch, to bring up the character menu. When you see that character menu, then select the black silhouette of the character you want from the grid and select “Buy” to make it available for you to play with in Free Play mode.
Important Note: Unlocking characters usually involves completing campaign missions, bonus- or side missions, or finding their token card hidden throughout the game levels or overworld map.